The present invention relates to a ratchet wrench and, more particularly, to a ratchet wrench preventing jam of pawls.
U.S. Pat. No. 6,981,434 discloses a wrench including a head having a through-hole receiving an engaging wheel. A recess is defined in an inner periphery of the through-hole and receives two pawls that can be actuated by a control member. The control member can change the positions of the pawls so that one of the pawls can engage with the engaging wheel to allow the engaging wheel to rotate in a single direction relative to the wrench, as shown in FIGS. 3, 6, and 7 of U.S. Pat. No. 6,981,434.
However, the wrench having two pawls of this type encounters difficulties in processing. With reference to FIG. 10 showing a portion of a wrench based on U.S. Pat. No. 6,981,434, the wrench 90 includes a head 90 having a through-hole 91 receiving an engaging wheel 92. A recess 93 is in communication with through-hole 91 and receives two pawls 93.
Offset of the recess 93 relative to through-hole 91 often occurs due to errors during processing of recess 93. Specifically, through-hole 93 defines a rotating axis CL about which engaging wheel 92 rotates. Recess 93 includes crescent cross sections having a central axis P0 that is preferably located on a reference line Y extending through rotating axis CL and spaced from another reference line X extending through rotating axis CL. However, the outer diameter of the cutter for processing recess 93 wears after processing a number of wrenches. The diameter of the new cutter is larger than that of the old cutter. As a result, recesses 93 of some wrenches are larger than others after processing.
Besides the above problem, each factor, including setting of the coordinate of the cutter, temperature control of the cutter and the wrench, the position of a clamp for clamping wrench 90, etc., affects the location of recess 93 of each wrench 90 after processing, such that processing errors occur easily. FIG. 10 shows central axes P1 and P2 of recess 93 offsetting from ideal central axis P0 along reference line Y and shows central axes P3 and P4 of the recess 93 offsetting from ideal central axis P0 along reference axis X.
The processing errors causing offsetting of recess 93 also result in poor engagement of pawls 94 with engaging wheel 92, leading to jam of pawls 94 between engaging wheel 92 and a wall of recess 93 such that both pawls 94 can not be moved. As a result, the product defect rate resulting from these processing errors can not be reduced, failing to meet the requirements of the market.
FIG. 10 shows wrench 90 in a natural position not engaged with a fastener, wherein pawls 94 are not moved, and the wall of recess 93 does not deform. A spring 95 biases left pawl 94 to press against a left wall section of recess 93 and to engage with engaging wheel 92. Spring 95 also biases right pawl 94 to press against a right wall section of recess 93 and to engage with engaging wheel 92. Nevertheless, both pawls 94 can still be disengaged from engaging wheel 92. In this case, pawls 94 are in a stable state in which two closest teeth respectively of pawls 94 have a safety spacing D1 therebetween. This is the ideal state of pawls 94.
In fact, the engagement between pawls 94 and engaging wheel 92 of a wrench 90 differs from that in another wrench 90 due to the processing errors. Wrenches 90 with poor engagement become defective. All of these result from the differing sizes or offsetting of recesses 93. FIGS. 11-13 show jam of pawls 94 due to offsetting from ideal central axis P0 to central axis P1 or P2.
With reference to FIG. 11, when wrench 90 is rotated counterclockwise to tighten a fastener 80, the reactive force from fastener 80 causes engaging wheel 92 to actuate left pawl 94 and to press against the left wall section of recess 93, causing deformation of the left wall surface 83. At this time, right pawl 94 gradually disengages from engaging wheel 92. With reference to FIG. 12, when the teeth of right pawl 94 are pushed outward by spring 95 and slip across the crests of the teeth of engaging wheel 92, spring 95 pushes right pawl 94 away from left pawl 94, such that right pawl 94 is moved through a distance equal to a tooth spacing between two adjacent crests of right pawl 94. With reference to FIG. 13, right pawl 94 is moved into and jams in a right corner of recess 93. At this time, left pawl 94 is pushed by the reactive force from the left wall section of recess 93, and this reactive force is transmitted through engaging wheel 92 to right pawl 94, such that right pawl 94 tightly presses against the right wall section of recess 93. As a result, both of left and right pawls 94 jam and, thus, can not be disengaged from engaging wheel 92. In this jammed state, the two closest teeth respectively of pawls 94 have a jam spacing D2 therebetween larger than safety spacing D1.
In an attempt to solve jam of pawls 94 by increasing the precision of the processing, the costs are significantly increased and not acceptable on the market. Furthermore, jam of pawls 94 also occurs due to other factors such as processing errors or positioning errors.
Thus, a need exists for a novel wrench capable of preventing jam of the pawls.